Differential Diagnosis
The patient's presentation is complex, with multiple symptoms and test results that need to be considered. Here's a breakdown of the differential diagnosis:
- Single Most Likely Diagnosis
- Cushing's Disease: The patient has an elevated ACTH level, a low-normal cortisol level, and a suppressed DST, which suggests Cushing's disease. The presence of a pituitary adenoma and symptoms such as weight gain and cushingoid features further support this diagnosis. The normal 24-hour urine cortisol may be seen in cyclic Cushing's disease.
- Other Likely Diagnoses
- Pseudo-Cushing's Syndrome: The patient's symptoms and laboratory results could also be consistent with pseudo-Cushing's syndrome, which is often seen in patients with polycystic ovary syndrome (PCOS), depression, or other conditions. The patient's use of oral combined BCP and problems with weight gain and loss could contribute to this diagnosis.
- Adrenal Insufficiency: Although the patient's cortisol level is low-normal, the elevated ACTH level could suggest adrenal insufficiency. However, the normal STIM test makes this diagnosis less likely.
- Do Not Miss Diagnoses
- Nelson's Syndrome: This is a rare condition that occurs in patients who have had bilateral adrenalectomy for Cushing's disease and subsequently develop a pituitary adenoma. Although the patient has not had adrenalectomy, it's essential to consider this diagnosis due to the presence of a pituitary adenoma and elevated ACTH level.
- Ectopic ACTH-Producing Tumor: Although rare, an ectopic ACTH-producing tumor could cause Cushing's syndrome. The patient's symptoms and laboratory results could be consistent with this diagnosis, and it's essential to rule it out.
- Rare Diagnoses
- Familial Cushing's Syndrome: This is a rare genetic disorder that causes Cushing's syndrome. Although the patient's family history is not provided, it's essential to consider this diagnosis in the differential.
- McCune-Albright Syndrome: This is a rare genetic disorder that can cause Cushing's syndrome, among other symptoms. The patient's symptoms and laboratory results could be consistent with this diagnosis, although it's rare and would require further evaluation.